You've probably seen Alexander Ludwig before--he's had roles in movies such as The Hunger Games and Grown Ups 2--but you've never seen him like this. He stars alongside Mark Wahlberg, our January/February cover guy, in Lone Survivor, and underwent a hefty transformation for his role in the film. Ludwig recently sat down with Men's Fitness to tell us about his workout routine leading up to the film, his partnership with fitness brand RYU, and what's next for his career.

Men's Fitness: For those who haven’t seen it yet, what is Lone Survivor about? What’s your role in the movie?

Alexander Ludwig: Lone Survivor is based on a true story about Marcus Luttrell, a Navy SEAL, and what he had to go through in Afghanistan while on a mission called Operation Red Wing. It’s a story about brotherhood and courage. I play Shane Patton, the youngest Navy Seal in the squadron. I’m Mark Wahlberg’s kind of younger brother character – everything [Shane] knows, he learned from Marcus. All he wants to do is to go on these missions with the boys and be part of the action. Basically, when all this stuff goes down in Afghanistan, Shane’s one of the main reasons they go to save these four guys. Obviously, things don’t go as they’d all hoped and it’s devastating, but it’s truly an incredible story about these real people who have to go through extraordinary circumstances to survive. It’s very intense.

Did you have to go through any special training for the movie?

Nothing compared to what those guys go through, but we did have Navy SEALs on set every day, coaching us through how they live their everyday lives. If we were doing anything wrong, they’d be there for us. I wanted to put on as much weight as I possibly could to make it look as real as possible. A lot of these guys aren’t skinny, normal-weight guys, and Shane definitely wasn’t, so I gained 30 pounds of muscle for this role. A lot of the workout regimen I actually developed myself. I didn’t have enough time between Grown Ups 2 and Lone Survivor to actually work with a trainer. I ate like a caveman–nutrition is so important. I ate lots of meat and vegetables. I did lots of heavy lifting–lower number of lifts and heavy weight. I did supersets of chest and I did this one ab workout I created. It was exhausting and gruesome. I’d work out six days a week. Every day I’d alternate among back, biceps, chest, and triceps, then legs.